Patent GB-735644-A (GB)
Title: Improvements in or relating to automatic copying machine with anticipator control
IPC: B23Q35/128
Filed: 1952-06-24
Abstract: 735,644. Electric copy milling machines. KEARNEY & TRECKER CORPORATION. June 24; 1952 [Sept. 17, 1951], No. 15866/52. Class 40 (1). [Also in Group XL (b)] In a copying machine, auxiliary control means associated with the feeler anticipates changes in the direction of relative movement between feeler and pattern, and modifies the feed rate of this movement which is normally substantially constant. The invention is described as applied to a copy milling machine using a light beam " feeler." Scanning, Figs. 7, 20, 23. As shown, the work 81 and a transparent sheet 65 carrying the opaque pattern, 78, are moved together in the co-ordinate directions East-West and North- South by respective D.C. reversible motors 53, 54 under the control of a fixed photo-electric scanner. Light from a lamp 122 after reflection at 127, 124 passes vertically downwards past the pattern edge through the transparent sheet 65 and the hollow shaft 72 of a motor 73 on to a photo-cell 137. The synchronous motor 73 drives a rotary shutter head 69 at constant speed, so that eccentrically disposed holes 74, 75 in the shutter produce two concentric annular scanning beams of light, the inner beam produced by the " copy " hole 74, controlling the co-ordinate drive motors during scanning of a straight or slightly curved edge, such as 79, of the pattern 78, and the outer beam formed by the anticipating shutter hole 75 superposing a further control on the appropriate co-ordinate motors as a sudden change in direction of the pattern edge being scanned is approached, e.g. the corner between edges 79, 80. A blanker disc 83 mounted concentrically above the shutter head 69 passes the inner annular copy beam through its central aperture 85 but blocks the outer anticipating beam except for that portion of the annular scan coincidental with a radial notch 86 extending from the circular aperture 85. The blanker disc 83 is set angularly through gearing 88 by a Selsyn receiver motor 91, rendered dead-beat by a braking generator 110 on its shaft, and energized in dependence on the armature energization of the main co-ordinate feed motors 53, 54, so that the radial notch 86 always faces in a direction opposite to the main feed direction of the pattern 78 and work 81. Thus, assuming the pattern 78, Figs. 7, 20, is being moved Westwards by the motor 53 and the edge 79 is being scanned, the radial notch 86 will face Eastwards and lie over the opaque pattern. Copy light pulses only are sent in this case, one per shutter revolution, to drive the E.-W. motor 53 to advance the pattern and the work. These conditions obtain until the pattern edge 80 approaches the scanning axis when anticipating light pulses of increasing duration are passed, one per shutter revolution, as the anticipating hole 75 overlaps the edge 80. These pulses decelerate, the pattern feed in the West direction as the pattern corner is approached to prevent overrun of the pattern. Finally, when the corner has been sensed by the copy hole 74 and the main feed of the pattern changed to South, Fig. 23, the blanking disc will have been rotated by the changed energization of the main feed motors so that the notch 86 faces North during copy scanning of the pattern edge 80. In this way the anticipating hole 75 functions only when a large directional change of the pattern edge being scanned is approached. Modified scanning arrangements, Figs. 29, 30. The rotating shutter may be mounted above the pattern support 65, Fig. 26 (not shown), and the blanker disc below it. The blanker disc may be dispensed with when the photo-cell is inverted in its function. The copy aperture 481 is then made of spiral form, Fig. 29, and may be combined with the anticipating aperture 486 by further enlarging the aperture as shown at 489, Fig. 30. Motor control circuits, Fig. 8. The photocell amplifier 143 has a normally non-conducting pentode 183, and a normally conducting pentode 184, light pulses falling on the photo-cell reversing these conditions to send amplified positive pulses over line 216, corresponding in duration and timing to the light pulses, to the grids of N.W.S.E. tubes 218-221, in a translator 144. The anodes of these four tubes are energized from the three phase mains 150 which also supply the shutter motor stator by a " Variac " (Registered Trade Mark) 240 and Scott connected transformers 237, so that the anodes are rendered positive sequentially in overlapping relationship and constitute a commutating timing circuit operating in synchronism with the rotating shutter head 69. Thus, those of the translator tubes which operate during each shutter cycle, and the timing of their operation, depends on the duration and phase position in the cycle of the light pulses. The translator tube outputs charge respective N.W.S.E. condensers 271-274 to apply corresponding signal voltage to the grids of N.W.S.E. thyratrons 296, 314, 297, 313, the plates of which are energized sequentially similarly to the translator tubes but by virtue of phase-shifters 360, 361 lead the corresponding translator tube anodes by 90 degrees. The thyratrons selectively control the E.-W. and N.-S. motors 53, 54. Negative feedback derived from the back e.m.f. of each feed motor by way of a potentiometer 326 together with a D.C. bias derived from a rectifier 338 and potentiometer 331 is injected in series with the signal voltage to the thyratron grids. The negative feedback enhances speed regulation of the motors and the D.C. bias ensures that D.C. pulses alternating in polarity and of low magnitude are continuously applied to the feed motor armatures when at rest to ensure instantaneous response thereof to a signal. The eccentricity of the shutter copy hole 74 and the motor control circuits are so arranged that the section of the pattern edge being scanned is maintained a predetermined distance from the shutter axis and that for each copy light pulse three of the thyratrons are energized. For example, in the case of the pattern edge 79 running E.-W., the W thyratron 314 would be energized once during each shutter cycle to produce Westwards pattern feed and both the N, S thyratrons 296, 297 would also be energized for equal times during each cycle, their resultant effect on the N.-S. motor being zero. Any slight deviation in the pattern edge direction would cause the N.-S. thyratrons to be energized for unequal periods during each cycle and so drive the N.-S. feed motor in the appropriate sense. Light pulses produced by the anticipating hole function in a similar way to energize three of the thyratrons per cycle to decelerate the pattern feed in the main direction so that the directional change in the pattern edge may be negotiated without overrun. To facilitate movement of the pattern into guiding relationship with the scanner, the feed motors may be selectively energized by a manuallyoperated toggle lever 381, operating switches 223-226 to actuate the associated translator tubes. The Selsyn motor 91 which adjusts the blanker disc has quadrature coils connected respectively across the armatures of the E.-W. and N.-S. feed motors so that the orientation of the blanker disc at all times bears the desired angular relationship to the pattern feed. The copy and anticipating holes 74, 75 together with the blanker disc may be pre-adjusted manually, Figs. 5, 6 (not shown), to cater for cutters of varying diameters. Modifications. When the photo-cell is inverted, Fig. 28 (not shown), for use with the modified scanning arrangements, two pentodes are again used in the photo-cell amplifier, one normally conducting and one non-conducting, this condition being reversed when light falls on the photo-cell to send negative pulses over the line 216 so that the translator tubes operate only when no light falls on the cell. The operation of the feed motors in this case is substantially as previously described. Ward- Leonard control may be used for the pattern feed motors, Fig. 27 (not shown).